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Gene Review

cysK  -  cysteine synthase A

Salmonella enterica subsp. enterica serovar Typhimurium str. LT2

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Disease relevance of cysK

  • This paper describes the characterisation of expression of the cysteine biosynthesis genes of Salmonella typhimurium, cysE, cysM and cysK, and linked cysEM, cysME and cysKE genes as transgenes in mice and sheep [1].

High impact information on cysK

  • Two 1,2,4-triazole-resistant strains bearing mutations in cysK, the structural gene for O-acetylserine sulfhydrylase A, incorporate only small quantities of O-acetyl-L-serine into 1,2,4-triazole-1-alanine in vivo [2].
  • A third mutant protein, CysB(W166R), was totally inactive at 10 mM MgCl2, but gave constitutive expression of the cysK and cysJIH promoters at 2 mM MgCl2 [3].
  • A third topology is present in the cysK and cysP promoters, where an additional half-site is oriented toward the activation site and separated from it by one helical turn [4].
  • CysB is known to bind to activation sites just upstream of the -35 regions of the positively regulated cysJIH, cysK, and cysP promoters and to a repressor site centered at about +1 in the cysB promoter [4].
  • The results give a gene order of cysA-cysM-crr-ptsl-ptsH-cysK over a distance of approximately 12 kilobases. cysM and cysA have been cloned and expressed in pBR322; attempts to obtain stable pBR322 derivatives carrying cysK were unsuccessful [5].

Associations of cysK with chemical compounds

  • The hydroxyl radical footprinting experiments reported here indicate that the activation sites CBS-J1, CBS-K1, and CBS-P1 in the cysJIH, cysK, and cysP promoters are composed of two convergently oriented 19-bp half-sites separated by 1 or 2 bp [4].
  • In vitro studies, using purified preparations of O-acetylserine sulfhydrylase A, revealed greater losses of triazolylase activity than sulfhydrylase activity in the enzymes from both cysK mutants [2].
  • Surprisingly, wild-type CysB was also constitutive for the cysK promoter at 2 mM mgCl2 but not at 10 mM MgCl2; it required inducer for cysJIH promoter activation at both concentrations [3].

Other interactions of cysK

  • These activities appear to be associated with the cysM gene, and this is able to be cotransducted with the cysK gene at a high frequency [6].


  1. Expression of bacterial cysteine biosynthesis genes in transgenic mice and sheep: toward a new in vivo amino acid biosynthesis pathway and improved wool growth. Bawden, C.S., Sivaprasad, A.V., Verma, P.J., Walker, S.K., Rogers, G.E. Transgenic Res. (1995) [Pubmed]
  2. Studies on the mechanism of inhibition of Salmonella typhimurium by 1,2,4-triazole. Kredich, N.M., Foote, L.J., Hulanicka, M.D. J. Biol. Chem. (1975) [Pubmed]
  3. In vitro characterization of constitutive CysB proteins from Salmonella typhimurium. Colyer, T.E., Kredich, N.M. Mol. Microbiol. (1996) [Pubmed]
  4. Hydroxyl radical footprints and half-site arrangements of binding sites for the CysB transcriptional activator of Salmonella typhimurium. Hryniewicz, M.M., Kredich, N.M. J. Bacteriol. (1995) [Pubmed]
  5. Cloning and characterization of the cysAMK region of Salmonella typhimurium. Hulanicka, M.D., Garrett, C., Jagura-Burdzy, G., Kredich, N.M. J. Bacteriol. (1986) [Pubmed]
  6. Evidence that thiosulfate assimilation by Salmonella typhimurium is catalyzed by cysteine synthase B. Nakamura, T., Kon, Y., Iwahashi, H., Eguchi, Y. J. Bacteriol. (1983) [Pubmed]
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